Lenvatinib is an oral multiple receptor tyrosine kinase (RTK) inhibitors for treating invasive and differentiated thyroid cancer developed by Eisai Co., and was approved on Feb. 13, 2015 by FDA. Lenvatinib mesylate is used in the approved drug. The chemical name of the drug is 4-{3-Chloro-4-[(cyclopropylcarbamoyl) amino]phenoxy}-7-methoxy-6-quinolinecarboxamide, and the structure is shown as formula I:

Since different crystalline forms of the same compound are different in solubility and stability, absorption and bioavailability, and therapeutic effect will be affected. Thus, a comprehensive and systematic polymorph and salts screening to select the most suitable crystalline form or salt form for development cannot be ignored.
CN1890220A disclosed crystalline Form A, Form B, Form C, Form F and Form I of lenvatinib mesylate. Form α and Form β of lenvatinib ethanesulfonate was also disclosed. The inventors of the present disclosure surprisingly find novel crystalline Form M of lenvatinib mesylate. Form M is different from any form disclosed in CN1890220A. In addition, Form M of lenvatinib mesylate of the present disclosure has good stability and remarkable purification effect in process. The process of novel crystalline forms is simple, low cost, and has an important value for future optimization and development of the drug.